If you don't want to download the OpenBSD src and patch your system all you really need are the new zoneinfo files:
Look at this article for the details: http://articles.techrepublic.com.com/5100-10877-6163042.html NOTE: The file to download from the ftp site is incorrect, it should be tzdata2007c.tar.gz I just did this on my OpenBSD 4.0 system and it worked perfectly :).
